1. Field of the Invention
The present invention relates to a laser processing method and a laser processing apparatus for processing very thin plate materials with laser beams.
2. Description of Related Art
Hard disk drives are improving in compactness, capacity and speed. To keep with this, head suspensions installed in the hard disk drives to support read/write elements are required to be compact, deal with high-density disks, operate at high speed, and reduce weight.
Reducing the weight of the head suspensions will be realized by thinning parts of the head suspensions. For this, foil-like materials of 10 to 15 μm thick are frequently used to produce the head suspensions.
In order to join such thin plate materials to each other, laser welding is used. The laser welding must be carried out with stabilized low output power to form nuggets for the thin plate materials. The nugget's diameter is dependent on the thicknesses of plate materials to be welded and is about 100 to 250 μm on the surface of the welded materials.
When laser-welding materials at multiple spots, a related art moves the materials or a laser emitter relative to the other so that a laser beam from the emitter is focused on a welding spot on the materials. Another related art employs a galvano-scanner or a galvano-mirror to focus a laser beam emitted from a laser emitter on a welding spot on the materials to be welded without moving the laser emitter or the materials, thereby speedily welding the materials at multiple spots and improving productivity.
The related arts, however, have a problem of causing plumes during the formation of nuggets, to destabilize the welding operation and fluctuate nugget diameters.
To solve this problem, Japanese Unexamined Patent Application Publication No. H03-234390 ('390 reference) discloses a technique of jetting an inert gas from a nozzle horizontally toward a welding part, to blow plumes out of the welding part.
The technique of the '390 reference is inapplicable to the galvano-scanner that discontinuously scans welding spots one after another at high speed on a material such as a head suspension because the technique is hard to synchronize the movement of the inert-gas-jetting nozzle with the high-speed movement of the galvano-scanner. Namely, it is difficult for the technique of the '390 reference to effectively jet the inert gas horizontally to each welding spot. Accordingly, the related art is incapable of stabilizing nugget diameters.
Japanese Unexamined Patent Application Publication No. 2003-251486 ('486 reference) discloses another technique that blows plumes out of a scan area.
This technique employs the galvano-scanner to guide a pulse laser beam through an fθ lens vertically to a welding spot on an object and accurately form a through hole or a via hole in the object. During the laser processing, the technique of the '486 reference horizontally jets a gas to blow plumes out of an entire scan area of the object that contains multiple spots to be laser-processed one after another.
According to the '486 reference, the scan area is open and the gas jetted to the scan area is drawn with a dust collecting nozzle. This related art gives no consideration on oxidization of the material to be laser-processed. If laser output power is adjustable, the related art may be applicable to welding thin plates instead of forming through holes or via holes in materials. The related art, however, is inapplicable to a product that allows no color change at welded spots, such as a head suspension because the related art has the oxidization problem.